The field of the present invention pertains to processes related to deposition of materials for fabricating semiconductors. More particularly, the present invention relates to the field of determining an end point for a remote microwave plasma cleaning system used to clean deposition equipment.
The power and usefulness of today""s digital integrated circuit (IC) devices is largely attributed to the increasing levels of integration. Electrical components such as resistors, diodes, transistors, and the like are created in the underlying chip, or IC, using photolithography and chemical vapor deposition (CVD). Photolithography defines the shape of a feature on the IC while the CVD is used to deposit an appropriate type of material on the wafer for the component or feature being generated
There is a continual motivation to reduce component size in order to increase the number of components on a given size of chip or die. A serious hindrance to proper performance of an IC is contamination of the IC at any stage of the fabrication process. Consequently, a need arises to reduce contamination during the fabrication of an IC.
One stage that can provide contamination is the CVD stage. In this stage, a wafer is place in a CVD chamber, a vacuum is established, and the appropriate materials are introduced into the chamber as a chemical vapor. These materials resultantly deposit on the wafer. However, these same materials also deposit on the equipment holding the wafer, namely the CVD chamber. Because the same chamber is used for repeated deposition operations on wafers, a buildup of deposition material occurs on the equipment. This buildup of material can be a source of contamination as the material sloughs off the chamber walls. One of the materials that build up on the CVD chamber walls is an oxide layer. Consequently, a need arises to remove the buildup of material on a CVD chamber wall arising from the deposition operation.
One conventional method of cleaning the CVD chamber walls remotely generates plasma using microwave energy. The plasma consists of fluorine radicals that are transported to the CVD chamber where they neutralize the oxide layer buildup on the CVD chamber. An important benefit of remote plasma generation is that it saves the CVD walls from ion energy bombardment and thus prevents damage to the chamber walls. However, a complementary weakness of remote plasma generation is that it provides no method of detecting the completion of cleaning the CVD chamber walls. That is, it is not possible to monitor the fluorine species in the chamber, which can signify an end point, when using remote plasma cleaning. Consequently, a need arises for a method to determine the end point of a remote cleaning operation.
Referring now to prior art FIG. 1, a graph 100 showing a conventional end point detection scheme for a remote cleaning operation is shown. Graph 100 has an abscissa of time 104 and an ordinate of layer thickness 102. Deposition operation 106, occurring over a period of time, results in a buildup of a layer thickness 103 on deposition equipment, such as the walls of a CVD chamber. After a sufficient layer of thickness 103 has built up, a cleaning operation 108 occurs over a period of time. Conventional methods have no method of determining the end point of the cleaning operation other than a simple timing operation. Consequently, after a predetermined amount of time 112 of exposing the deposition chamber to one of many different possible cleaning rates, e.g. rate A 110a or rate B 110b, the cleaning operation ceases. However, if the length of time for cleaning, or if the rate of cleaning, is not appropriate for the layer thickness built up on the CVD chamber walls, an underclean condition or an overclean condition will exist.
More specifically, underclean condition is represented in prior art FIG. 1 by a residual layer 116 remaining on the CVD chamber walls. In an underclean condition, contaminant may still exist in the CVD chamber, thus risking the integrity of any subsequent deposition operation for an IC. Alternatively, an overclean condition is represented by overclean layer thickness 118, which actually represents a removal of base material from the CVD chamber walls. In this latter scenario, the CVD chamber walls are damaged from overcleaning. Due to the expensive cost of replacement, overcleaning a CVD chamber is an undesirable condition. Because of the detrimental effects of both undercleaning and overcleaning, a need arises for very accurate method of determining when a remote cleaning operation has been completed on a CVD chamber wall.
In summary, a need arises to reduce contamination during the fabrication of an IC. Subsequently, a need arises to remove the buildup of material on a CVD chamber wall arising from the deposition operation. Additionally, a need arises for a method to determine the end point of a remote cleaning operation. Finally, a need arises to very accurately determine when a remote cleaning operation has been completed on a CVD chamber wall, because of the detrimental effects of both undercleaning and overcleaning.
The present invention provides a method to reduce contamination during the fabrication of an IC. More specifically, the present invention provides a method to accurately remove the buildup of material on a CVD chamber wall arising from the deposition operation. The present invention does so by providing a method to determine the end point of a remote cleaning operation. In particular, the present invention provides such an accurate method of determining when a remote cleaning operation has been completed on a CVD chamber wall that it substantially eliminates the detrimental effects of both undercleaning and overcleaning.
Specifically, one embodiment of the present invention provides a method of determining an end point for a remote microwave plasma cleaning system. In one embodiment, the method comprises several steps. The first step is to expose a capacitive electrical device to the deposition operation that the CVD chamber is exposed to between cleanings. Next, the capacitive electrical device, e.g. a capacitor, is exposed to a plasma cleaning operation that the CVD chamber likewise encounters. A capacitive performance characteristic of the capacitor is measured during the cleaning operation. In the last step, an amount of cleaning performed on the capacitor is calculated based on a relationship between a baseline value of the performance characteristic and on the measured value of the performance characteristic of the capacitor. The baseline value represents the capacitive performance characteristic of the capacitor without the deposition layer, and can indicate that the cleaning is completed. This method estimates that the cleaning effectiveness on the electrical device is approximately equivalent to the cleaning effectiveness on the CVD chamber walls. If the end point of the cleaning arises, then an indication is provided.
Another embodiment of the present invention implements the comparison operation in a variety of embodiments. In one embodiment, the comparison operation is performed by a processor coupled to memory. The processor performs the steps of comparing the baseline value with a measured value of the performance characteristic of the capacitive electrical device during the cleaning operation. In another embodiment, the comparison operation is performed by an analog operational amplifier.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawing figures.